During T cell development and regulation of immune responses, negative control mechanisms ensure that autoreactive or nonfunctional T cells are deleted and excessive expansion of peripheral T cells is prevented. Elimination of immature thymocytes and mature peripheral T cells occur via induction of programmed cell death, apoptosis, in which the cytoplasm of the affected cells condenses, the plasma membrane becomes convoluted, the nucleus condenses, and DNA fragmentation occurs. Prior art data suggest two pathways by which apoptosis of T cells may be induced. One pathway may involve stimulation of the CD3 T-cell receptor (TCR) complex. The other pathway may involve the cell surface Fas antigen. Fas is a member of the nerve growth factor/tumor necrosis factor receptor superfamily. Watanabe-Fukanaga et al. (J. Immunol. 148: 1274-79 (1992)) and Itoh et al. (Cell 66: 233-43 (1991)) have reported cloning of cDNA encoding murine and human Fas antigen, respectively.
Mice homozygous for the autosomal recessive mutation known as the lymphoproliferation (lpr) mutation have defects in the Fas antigen gene and do not express normal functional Fas protein capable of transducing the apoptotic signal (Watanabe-Fukunaga et al., Nature 356: 314-17 (1992)). These mice develop disorders characterized by the accumulation of CD4.sup.- CD8.sup.- T cells in lymph nodes and the spleen, hypergammaglobulinemia, autoantibody production, rheumatoid factor, arthritis and glomerulonephritis. Id.
Other mice homozygous for a mutant gene known as the generalized lymphoproliferative disease (gld) mutation exhibit a clinical syndrome indistinguishable from that found in lpr mice (J. B. Roths et al., J. Exp. Med., 159: 1-20 (1984)). The gld gene maps to mouse chromosome 1 whereas lpr gene maps to mouse chromosome 19. Although the product of the gld gene has not been isolated., Allen et al. (J. Exp. Med., 172: 1367-75 (1990)) have suggested that lpr and gld genes encode an interacting ligand-receptor pair of molecules expressed on different cells.
The Fas antigen was originally defined by two monoclonal antibodies, CH-11 and anti-APO-1. CH-11 belongs to the IgM class of immunoglobulins. Anti-APO-1 belongs to the IgG3 class of immunoglobulins. Both CH-11 and anti-APO-1 monoclonal antibodies bind to cells expressing human Fas, work as agonists, and induce apoptosis in lymphoid cell lines expressing Fas. Both CH-11 and anti-APO-1 antibodies were selected based upon their cytolytic activity towards certain in vitro cultured cell lines.
Monoclonal antibodies that block binding of CH-11 to cells expressing Fas antigen or that block CH-11-mediated or Fas-L-mediated lysis of lymphoid cell lines have not yet been disclosed. Such blocking antibodies would be useful, for example, in research applications to provide insight into its role in normal immune responses as well as in the generation of autoimmune diseases. Blocking antibodies also would be useful in therapeutic applications requiring inhibition of Fas- or Fas L-mediated biological activity.
The present invention provides such antibodies and other related advantages.